/Engine/Source/Runtime/GeometryCore/Public/Util/IndexUtil.h
the vertex that is the same in both EdgeVerts1 and EdgeVerts2, or InvalidID if not found
namespace IndexUtil { int IndexUtil::FindSharedEdgeVertex ( const [FIndex2i](API\Runtime\GeometryCore\FIndex2i) & EdgeVerts1, const [FIndex2i](API\Runtime\GeometryCore\FIndex2i) & EdgeVerts2 ) }